U.S. patent application Ser. No. 12/916,984 (which has been incorporated herein by reference) has been published as United States Patent Application Publication No. 2011/0100874. The reader is presumed to be familiar with the disclosure of this published application. This published application will be referred to herein as the “874 application.”
U.S. Pat. No. 8,088,270, which is expressly incorporated herein by reference, relates to a “Process For Recovering Alkali Metals And Sulfur From Alkali Metal Sulfides And PolySulfides.” The reader is presumed to be familiar with the disclosure of this published patent. This published patent will be referred to herein as the “'270 patent.”
The demand for energy and the hydrocarbons from which that energy is derived is continually rising. The hydrocarbon raw materials used to provide this energy, however, can contain difficult to remove sulfur and metals that hinder their usage. Sulfur can cause air pollution, and can poison catalysts designed to remove hydrocarbons and nitrogen oxide from motor vehicle exhaust. Similarly, other (heavy) metals contained in the hydrocarbon stream can poison catalysts typically utilized for removal of sulfur.
Extensive reserves of shale oil exist in the U.S. that will increasingly play a role in meeting U.S. energy needs. Over 1 trillion barrels reserves lay in a relatively small area known as the Green River Formation located in Colorado, Utah, and Wyoming. As the price of crude oil rises, these shale oil resources become more attractive. However, technical issues surrounding this shale oil remain to be solved. For example, this shale oil has a relatively high amount of nitrogen contained therein (in addition to high levels of heavy metals and sulfur). Shale oil characteristically is high in nitrogen, sulfur, and heavy metals which makes subsequent hydrotreating difficult. According to America's Strategic Unconventional Fuels, Vol. III—Resource and Technology Profiles, p. 111-25, nitrogen is typically around 2% and sulfur around 1% in most samples of shale oil (Heavy metals are also present.) Heavy metals contained in shale oil pose a large problem to upgraders trying to upgrade this shale oil for commercial use. For example, sulfur and nitrogen typically are removed from the shale oil via hydrotreating at elevated temperatures and pressures using catalysts such as Co—Mo/Al2O3 or Ni—Mo/Al2O3. However, such catalysts are deactivated (poisoned) by the presence of heavy metals as the heavy metals operate to mask the catalysts.
Another example of a source of hydrocarbon fuel where the removal of sulfur poses a problem is in bitumen existing in ample quantities in Alberta, Canada and heavy oils such as in Venezuela. In order to remove sufficient sulfur from the bitumen for it to be useful as an energy resource, excessive hydrogen must be introduced under extreme conditions, which creates an inefficient and economically undesirable process.
Over the last several years, sodium has been recognized as being effective for the treatment of high-sulfur petroleum oil distillate, crude, heavy oil, bitumen, and shale oil. Sodium is capable of reacting with the oil and its contaminants to dramatically reduce the sulfur, nitrogen, and metal content through the formation of sodium sulfide compounds (sulfide, polysulfide and hydrosulfide). Examples of the processes can be seen in U.S. Pat. Nos. 3,785,965; 3,787,315; 3,788,978; 4,076,613; 5,695,632; 5,935,421; and 6,210,564. This process is further described in the '874 application.
When shale oil, heavy oil or bitumen or other oil feedstock is reacted with the alkali metals, this reaction occurs generally at a temperature between 150-450° C. This reaction is also performed at a pressure that is anywhere between atmospheric pressure and 2000 psi. For example 2 moles alkali metal and 1 mole hydrogen (H2) may be needed per mole sulfur according to the following initial reaction:R—S—R′+2M+H2→R—H+R′—H+M2S,
Where M is an alkali metal such as sodium or lithium and 3 moles alkali metal and 1.5 moles hydrogen (H2) may be needed per mole nitrogen according to the following initial reaction:R,R′,R″—N+3M+1.5H2→R—H+R′—H+R″—H+M3NAlternatively, the '874 application describes a method of upgrading an oil feedstock (such as heavy oil, shale oil, bitumen, etc.) by combining the oil feedstock with an alkali metal and an upgradant hydrocarbon material. This reaction operates to remove the sulfur, nitrogen and/or heavy metals contained within the oil feedstock.
It should also be noted that heavy metals contained in the shale oil may also be removed via the use of alkali metals such as sodium. Heavy metals contained in organometallic molecules such as complex porphyrins are reduced to the metallic state by the alkali metal. Once the heavy metals have been reduced, they can be separated from the oil because they no longer are chemically bonded to the organic structure. In addition, once the metals are removed from the porphyrin structure, the nitrogen heteroatoms in the structure are exposed for further denitrogenation.
The following is a summary of the reaction of shale oil, bitumen and/or other oil hydrocarbons when they are reacted with alkali metals, such as lithium or sodium. Liquid phase alkali metal is brought into contact with the organic molecules containing heteroatoms and metals in the presence of hydrogen, methane, and also gases such as nitrogen (or inert gases such as helium, neon, argon, krypton, xenon and radon). The free energy of reaction with organic sulfur, organic nitrogen and organic heavy metals is stronger with alkali metals than with hydrogen, so the reaction more readily occurs without full saturation of the organics with hydrogen. (Hydrogen is generally used in the reaction to cap broken bonds previously attached to heteroatoms and metals, prevent carbon-carbon bonds from forming or coking.) Once the alkali metal compounds are formed and heavy metals are reduced to their metallic states, it is necessary to separate these products from the hydrocarbon materials. A gravimetric separation, such as centrifugation or filtering, can separate the organic, upgraded oil, from the salt phase, metallic phase, and organic solids which may be formed.
Once the alkali metal sulfide has been separated from the oil, sulfur and metals are substantially removed, and nitrogen is moderately removed. Also, both viscosity and density are reduced, while the API gravity is increased. Bitumen or heavy oil would be considered synthetic crude oil (SCO) and can be shipped via pipeline for further refining. Similarly, shale oil will have been considerably upgraded after such processing. Subsequent refining will be easier since the troublesome metals have been removed.
Although the effectiveness of the use of alkali metals such as sodium in the removal of sulfur has been demonstrated, the process is not commercially practiced because a practical, cost-effective method to regenerate the alkali metal has not yet heretofore been proposed. Several researchers have proposed the regeneration of sodium using an electrolytic cell, which uses a sodium-ion-conductive beta-alumina membrane. Beta-alumina, however, is both expensive and fragile, and no significant metal production utilizes beta-alumina as a membrane separator. Further, the cell utilizes a sulfur anode, which results in high polarization of the cell causing excessive specific energy requirements.
Metallic sodium is commercially produced almost exclusively in a Downs-cell such as the cell described in U.S. Pat. No. 1,501,756. Such cells electrolyze sodium chloride that is dissolved in a molten salt electrolyte to form molten sodium at the cathode and chlorine gas at the anode. The cells operate at a temperature near 600° C., a temperature compatible with the electrolyte used. Unlike the sulfur anode, the chlorine anode is utilized commercially both with molten salts as in the co-production of sodium and with saline solution as in the co-production of sodium hydroxide.
Another cell technology that is capable of producing sodium metal at a temperature of less than 200° C. has been disclosed by Jacobsen et al. in U.S. Pat. No. 6,787,019, and Thompson et al. in U.S. Pat. No. 6,368,486. In those disclosures, low temperature co-electrolyte is utilized with the alkali halide to form a low temperature melting electrolyte.
Accordingly, the present embodiments are designed to provide a cost-effective and efficient method for the regeneration of alkali metals used in the desulfurization, denitrogenation, and demetallation of hydrocarbon streams. As will be described herein, the present invention is able to remove contaminants and separate out unwanted material products from desulfurization/denitrogenation/demetallation reactions, and then recover those materials for later use.